Take out charger, then battery, and hold down power button for 20 seconds, insert battery, then charger and make sure charger is plugged into main power supply and not extension cord plug etc.
If that doesnt work either your screen is bad or your power button is damaged or has loose connections , the latter being the probable cause. Try opening the laptop very carefully using the iFixit guide for your model (if availaible) or google a "Model opening video" to get a full video on how to open your laptop.